1. Field of the Invention
This invention relates to the determination of the shape of rigid or nearly rigid bodies. More particularly, this invention relates to shape determination of such bodies using a computer navigation system.
2. Description of the Background of the Invention
Computer determination of the location of bodies has been used in manufacturing and medical fields for a number of years. Computer navigation requires that the bodies to be tracked by the navigation system have a known shape, so that the orientation and position of the bodies can be properly tracked by the system. Tracking is accomplished by either attaching a tracking device to the body or embedding the tracking device into the body. There are numerous tracking technologies including active and passive optical tracking systems, magnetic systems and inertial systems.
For many applications it is necessary to field calibrate bodies so that the navigation system can thereafter track the body and realistically render the body graphically on a computer display. Typically, this is done by attaching the tracking device in a fixed relation with the body and then inserting the body into a calibration device. These devices can be as simple as a divot in a known relation to the navigation system or can be a device that constrains the body in a predetermined attitude relative to the navigation system with the tip of the body located in a predetermined position. Current tracking calibration requires some physical contact between the body and a calibration device.
For certain situations, it may be desirable to minimize contact with other devices or bodies. For instance in a surgical setting, sterility requirements require that the body to be used be sterile and that every body it contacts in any way also be sterile. This necessitates sterilizing the calibration device and maintaining the calibration device within the sterile field. With space at a premium in a surgical suite, this can be a problem.
In addition, bodies that include attachments, such as screwdrivers, drills, implant insertion devices, etc., need to be recalibrated each time a new attachment is inserted. Lastly, some devices do not have an axial shape with the result that these bodies have been difficult to field calibrate using known methods.